The long term goal of our proposed research is to account for the role of the HIV-1-specific protein Vpu in viral replication. In particular, we will carry out experiments to determine the mechanism by which Vpu facilitates release of particles from infected cells. Two of the specific aims of this proposal are directed at understanding how Vpu interacts with particular factors in the infected cell. Our preliminary observations indicate that Vpu is dispensable for HIV-1 production from a simian cell type, but that Vpu is necessary for efficient virus production and interacts specifically and directly with two proteins expressed in human lymphocytes. Therefore, we will try to determine whether interaction between Vpu and these proteins leads to expedited particle release and whether there are qualitative and/or quantitative differences between these proteins in simian versus human cells. Our preliminary results indicated that some cell types are intolerant to Vpu expression, and eventually expire, while others are refractory to Vpu expression. There is possible correlation between this sensitivity or refractoriness to Vpu expression and our observed cell type specificity of Vpu-facilitated particle release. In addition to our preliminary data indicating that specific cellular factors are involved in Vpu action, other of our data suggests that Vpu can interact specifically with the Gag precursor protein. We plan to examine the role of this possible interaction in Vpu function. Finally, we will carry out experiments to determine the relationship between particle release and a second activity of Vpu; by understanding the mechanism by which Vpu promotes efficient particle release it might be possible to determine whether dissociation of intracellular CD4-Envelope glycoprotein complexes, mediated by Vpu, is mechanistically linked to particle release. Since Vpu is intrinsically required for the genesis of progeny of HIV-1 particles in virus-producing cells, understanding the role of Vpu in HIV-1 particle is fundamentally important in arriving at a comprehensive view of HIV-1 particle release. A clear general picture of particle formation and release, and a specific understanding of the role of Vpu, are likely to suggest novel targets to abrogate virus replication.